Automated machine tool lines became popular in heavy industry during the 1940's and 1950's, particularly in the automobile industry. These lines include machine tools spaced within the plant with conveyors extending between the tools for advancing work pallets having automobile parts thereon such as cylinder blocks or crank shafts from one machine to another without the interposition of any human manipulation. These pallets are usually evenly spaced upon the conveyor so that they can be indexed in step-by-step fashion simultaneously from one machine to another. When all of the machining operations at all the tools were completed, the work pieces were advanced one step and the process then repeated.
This system had the disadvantage that the machining time for the entire system was dependent upon and controlled by the machining time of the slowest machine on the line. The resulting disadvantage of this system, of course, is in hindsight the obvious resulting high machining costs.
To attempt to obviate these problems, many systems were developed only some of which have gained any significant commercial recognition. One solution is to provide what is termed a "universal machine" that can be programmed to perform the function of either a broken machine on the line or to share time on the line with the slowest machine on the line. This requires additional conveyor structure for alternately routing workpieces either on an alternate basis with the slowest machine, or on a permanent basis to the universal machine when one machine is completely down. Such a system significantly improves multiple machine tool line efficiency, but the basic slowness and delays created by step-by-step indexing of pallets continues to result in slow line performance. The reason for this is that even if the slow machine is assisted by a "universal machine", the next slowest machine, which may be only very slightly faster than the slow machine, controls the cycle time of the entire line. While additional "universal machines" may be provided to attempt to solve this problem, the provision of more machines results in diminishing returns from an economic viewpoint.
In recognizing these problems, there have been proposed in the last decade systems in which the work carriers "float" on the conveyor line and are not restricted to step-by-step indexing. The pallets may collect at any given work station merely on the basis of their own intelligence of what is happening at that station quite apart from the machine cycle times of any other station. This permits the faster machines to operate extremely efficiently with the workpieces collecting at the slower machines. With appropriate alternate route conveying to bypass the slower machine in such an instance to other machines under computer control, the efficiency of the overall line is greatly enhanced.
Turning to the prior art of specific conveyor structure, tilted rollers have been used in the past for conveying cylindrical workpieces but this prior art is only remotely relevant to the present conveyor environment. For example, in the Dreher U.S. Pat. No. 3,718,247 three driven rotating rollers, positioned on tilted axes, engage the exterior surface of a cylindrical tube and cause the tube to move axially. A similar system is shown in the Hamilton U.S. Pat. No. 3,642,041.
Other fringe prior art includes a linear actuator made by Barry Wright Corporation called a "Roh-lex" linear actuator which uses rollers engaging the exterior surface of a rotating rod to move a carriage. This arrangement is shown in U.S. Pat. No. 3,272,021. My U.S. Pat. No. 3,591,241 relating to vehicle drives shows tilted rollers for driving a vehicle.
It is a primary object of the present invention to provide a "floating" conveyor system of the type described that permits workpieces to move rapidly through the faster work stations and to collect at the slower work stations or other junction points.